Answer

Per the codes - R20 interior + R5 continuous exterior for the walls. With that as many building scientists will tell you following that will lead to issues especially if one is using fiberglass inside due to dew point issues. Many would say 1/4 to 1/2 of the total insulation R Value should be outside the structure) Going with closed cell throughout you could possibly eliminate the exterior (assuming the building inspector approves) if you fill the cavities completely & do a great job air sealing the rest of the areas (sill plates, top, seams, penetrations in wall, floor, attic, etc...) At minimum that would get you an R32 for the cavities. One big issue you also must take into account is each bathroom & kitchen must not only be vented to the exterior but they must also be used to help keep the Humidity levels down around the 40% mark. Basement floors should not be insulated unless you are running radiant heat - it is the walls that need it & you are looking at an R15 at minimum if continuous. I would also recommend following that through on the crawlspace walls also and eliminate venting creating a "sealed crawl" By doing this properly, following the rest of the codes, making sure you manage the moisture you should have a much more comfortable home with a lot less issues and lower heating costs.

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